On Mon, Mar 11, 2013 at 03:15:08PM -0600, Tim Gardner wrote:
> rpcrdma_register_default_external() is several frames into the call stack which
> goes deeper yet. You run the risk of stack corruption by declaring such a large
> automatic variable, so move the array of 'struct ib_phys_buf' objects into the
> transport structure 'struct rpcrdma_xprt' (which is dynamically allocated) in
> order to silence the frame-larger-than warning. Access to each struct
> rpcrdma_xprt is serialized by XPRT_LOCKED in xprt_reserve_xprt(), so there is
> no danger of multiple accessors to the array of struct ib_phys_buf objects.
>
> net/sunrpc/xprtrdma/verbs.c: In function 'rpcrdma_register_default_external':
> net/sunrpc/xprtrdma/verbs.c:1774:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>
> gcc version 4.6.3
>
> Cc: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
> Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Tom Tucker <tom@xxxxxx>
> Cc: Haggai Eran <haggaie@xxxxxxxxxxxx>
> Cc: Or Gerlitz <ogerlitz@xxxxxxxxxxxx>
> Cc: Shani Michaeli <shanim@xxxxxxxxxxxx>
> Cc: linux-nfs@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Tim Gardner <tim.gardner@xxxxxxxxxxxxx>
> ---
> v1 - Use kmalloc() to dynamically allocate and free the array of 'struct
> ib_phys_buf' objects
>
> v2 - Move the array of 'struct ib_phys_buf' objects into struct rpcrdma_req
> and pass this request down through rpcrdma_register_external() and
> rpcrdma_register_default_external(). This is less overhead then using
> kmalloc() and requires no extra error checking as the allocation burden is
> shifted to the transport client.
>
> v3 - Move the array of 'struct ib_phys_buf' objects into struct rpcrdma_xprt.
> Pass a pointer to this transport structure into rpcrdma_register_default_external().
> This is less overhead then using kmalloc() and requires no extra error checking
> as the allocation burden is shifted to the transport client.
Looks good to me; wish we could get it tested....
In future if we do decide to also increase the size of that array we may
need to allocate it separately from struct rpcrdma_xprt itself, which
looks already fairly large without it; on x86_64:
$ gdb net/sunrpc/xprtrdma/xprtrdma.ko
...
(gdb) p sizeof(struct rpcrdma_xprt)
$1 = 2912
But that shouldn't be a big deal to do.
--b.
>
> net/sunrpc/xprtrdma/verbs.c | 10 ++++++----
> net/sunrpc/xprtrdma/xprt_rdma.h | 5 ++++-
> 2 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 93726560..c7aa3da 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -1730,13 +1730,14 @@ rpcrdma_deregister_memwin_external(struct rpcrdma_mr_seg *seg,
> }
>
> static int
> -rpcrdma_register_default_external(struct rpcrdma_mr_seg *seg,
> - int *nsegs, int writing, struct rpcrdma_ia *ia)
> +rpcrdma_register_default_external(struct rpcrdma_xprt *r_xprt,
> + struct rpcrdma_mr_seg *seg, int *nsegs, int writing,
> + struct rpcrdma_ia *ia)
> {
> int mem_priv = (writing ? IB_ACCESS_REMOTE_WRITE :
> IB_ACCESS_REMOTE_READ);
> struct rpcrdma_mr_seg *seg1 = seg;
> - struct ib_phys_buf ipb[RPCRDMA_MAX_DATA_SEGS];
> + struct ib_phys_buf *ipb = r_xprt->ipb;
> int len, i, rc = 0;
>
> if (*nsegs > RPCRDMA_MAX_DATA_SEGS)
> @@ -1827,7 +1828,8 @@ rpcrdma_register_external(struct rpcrdma_mr_seg *seg,
>
> /* Default registration each time */
> default:
> - rc = rpcrdma_register_default_external(seg, &nsegs, writing, ia);
> + rc = rpcrdma_register_default_external(r_xprt, seg, &nsegs,
> + writing, ia);
> break;
> }
> if (rc)
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index cc1445d..d7b440f 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -269,7 +269,8 @@ struct rpcrdma_stats {
> * for convenience. This structure need not be visible externally.
> *
> * It is allocated and initialized during mount, and released
> - * during unmount.
> + * during unmount. Access to this structure is serialized by XPRT_LOCKED
> + * in xprt_reserve_xprt().
> */
> struct rpcrdma_xprt {
> struct rpc_xprt xprt;
> @@ -279,6 +280,8 @@ struct rpcrdma_xprt {
> struct rpcrdma_create_data_internal rx_data;
> struct delayed_work rdma_connect;
> struct rpcrdma_stats rx_stats;
> + /* temp work array */
> + struct ib_phys_buf ipb[RPCRDMA_MAX_DATA_SEGS];
> };
>
> #define rpcx_to_rdmax(x) container_of(x, struct rpcrdma_xprt, xprt)
> --
> 1.7.9.5
>
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